1. Field of the Invention
The present invention relates to a wheel speed sensor for a vehicle which has a function of preventing a coil open circuit.
2. Description of the Related Art
Generally, a wheel speed sensor is installed at a position adjacent to a sensor rotor of a hub in a vehicle. When a vehicle brakes, the wheel speed sensor detects revolutions of the wheel and outputs a signal indicating the detected revolution of the wheel. This signal is applied to a control unit and then the control unit provides uniform braking power on the basis of the signal.
Various techniques for the wheel speed sensor of a vehicle have been proposed. One approach, an electrical measuring instrument with connecting cable, has been proposed on U.S. Pat. No. 4,652,818 issued to Emil Buchschmid on May 24, 1987. Since this electrical measuring instrument is constituted of two housings, a bonding agent in order to assemble the housings together must be used. Consequently, the durability of the electrical measuring instrument deteriorates.
Next, U.S. Pat. No. 5,039,942 issued to Emil Buchschmid on Aug. 13, 1991 discloses a cable supporting insert for closing an opening in the housing of an inductive rotational speed sensor. However, in this cable supporting insert, a coil may be broke owing to minute movement of a permanent magnet during the manufacturing process of the housings by using an injecting molding technique.
Also, U.S. Pat. No. 5,254,807 issued to Werner Pfander on Oct. 19, 1993 discloses a sensor,. in particular RPM sensor. Since the sensor is constituted of two housings, a bonding agent in order to assemble the housings together must be used. Consequently, the durability of the sensor deteriorates.
Meanwhile, U.S. Pat. No. 5,493,217 issued to Ulrich Stahi on Feb. 24, 1996 discloses a longer-lasting inductive sensor with an electrical coil, having improved load-bearing and thermal properties. However, the coil of this inductive sensor may easily break when a conductive area having a wound coil is folded up.
The present invention solves the foregoing problems. It is an object of the present invention to provide a wheel speed sensor for a vehicle which has a function of preventing a coil open circuit.
It is another object of the present invention to provide a wheel speed sensor for a vehicle capable of having enhanced durability.
In order to achieve the above objects, the present invention provides a wheel speed sensor for a vehicle which has a function of preventing a coil open circuit, the wheel speed sensor comprising:
a bobbin having a coil winding part which is formed at a one end of the bobbin to become one body with the bobbin, a flange which is formed at a front portion of the coil winding part to become one body with the coil winding part, a guiding protrusion protruding from an upper portion of the coil winding part, and guiding bosses outwardly protruding from an outer periphery surface of the bobbin in the radial direction so that the coil directly passes by the guiding bosses, in which an inserting groove is formed along a circumference of the flange;
a lead frame member having a first lead frame, a second lead frame and a third lead frame, which are longitudinally arranged on the outer periphery surface of the bobbin, wherein the third lead frame protrudes from one side surface of the first lead frame, one end of the second lead frame is fixed to the surface of the bobbin and the other end of the second lead frame is perpendicular to the surface of the bobbin,
the coil is wound around the other end of the second lead frame, the other end of the second lead frame is folded toward the third lead frame, and one end of the third lead frame is folded toward the second lead frame in order to press the second lead frame; and
an injected, molded housing member for enclosing the bobbin and the lead frame member,
whereby the coil becomes relaxed when the second lead frame is folded toward the third lead frame.
A rubber ring is fitted into the inserting groove to cause close contact with the inner side of the housing.
As described above, in a wheel speed sensor for a vehicle which has a function of preventing a coil open circuit according to the preferred embodiment of the present invention, guiding bosses outwardly protrude from the outer periphery surface of the bobbin in the radial direction so that the coil may be directly passed by the guiding boss. Further, a housing encloses the first lead frame, the second lead frame and the third lead frame. In addition, a rubber ring is fitted into the inserting groove to cause contact with the inner side of the housing. With this structure, the wheel speed sensor can prevent a coil open circuit with the aid of the guiding boss.